Three years ago I started writing a novel about a man haunted by the absence of his ­father. He stalks his lovers, lives in his houses and wears his clothes. He is a most faithful son. And now, weeks from finishing that novel, I learn that my father, who disappeared 20 years ago, might be alive. Someone saw him in a secret political prison in Tripoli. "He is well. Frail, but well," was the man's message. He saw my father in 2002, but only recently was he able to send me the message. This is tremendous news. Tremendous in the way a storm or a flood can be tremendous.

Uncanny how reality presses against that precious quiet place of dreaming. As if life is jealous of fiction.

In March 1990, Egyptian secret service agents abducted my father from his home in Cairo. For the first two years they led us to believe that he was being held in Egypt, and told us to keep quiet or else they could not guarantee his safety. In 1992 my father managed to smuggle out a letter. A few months later my mother held it in her hand. His careful handwriting curled tightly on to itself to fit as many words as possible on the single A4 sheet of paper. Words with hardly a space between, above or beneath them. No margins, they run to the brink.

"Give me your hand: you are now within a foot / Of the extreme verge," Edgar says to his blind father in King Lear. How many words do you need to say everything? How many words before the verge?

I have imagined my father composing this letter in his head, reciting it in a whisper as he paced the "concrete room" during those precious, silent hours between midnight and early morning when the loudspeaker in the centre of the ceiling stopped its relentless blaring out of revolutionary songs and speeches. With paper being scarce, he must have rehearsed what he was going to write, committed it to memory as he did countless poems. His prose is even more measured than usual. Composure and control to crack the heart. He quoted from books, as if to say "I am still here, still part of the world". He offered precise and useful advise to my brother and me: "If you embark on a venture and it fails, move on to something else." And "An honest profit should never exceed 30%." He apologised to his wife for all that she had to go through. He apologised to my brother and to me. But then he said if he had it all to do again he would have walked the same path. "One day justice will be done and the jailer will replace the jailed."

Over the years I have met several former prisoners who were there when my father was first taken to Abu Salim, in Tripoli, in March 1990. When the news made the rounds that Jaballa Matar had been captured, several ­prisoners began ululating. A mournful cry intended both as defiance to the oppressor, and as comfort to a man they regarded as their leader. My ­father seemed to have accepted this role. One former prisoner had witnessed him strike back at a torturer. "A futile retaliation," the man told me, "but the news ran like wildfire in the prison and bolstered our hearts." I have had nightmares about what happened next, the moment after the ­"futile ­retaliation". This is perhaps why I am by nature unenthusiastic about such acts of heroism. I am as proud of his heroism as I begrudge the circumstances that demanded it. How often had I yearned for a pro­vincial man as father, growing old in his house.

The only other letter he managed to smuggle out to us was in 1995. Then in April 1996 the guards came and moved him and his companion Izzat al-Megaryef, a political dissident who was handed over by the Egyptians on the same day and in the same way. The two men were moved, it is not clear where. Their few belongings – cigarettes, a radio, clothes – turned up in the black market run by the guards. Two months later, in June 1996, a massacre took place in the same prison. Libyan authorities shot dead approximately 1,200 political prisoners. Guards went from cell to cell with a list of names. More prisoners were bussed in and deposited in the open courtyard of Abu Salim prison. Then gunfire.

How many bullets do you need to kill 1,200 men?

How many bullets per head should you budget for?

The shooting went on for six hours. One prisoner described it as "a drill ­inside your head". And when I first heard this I thought: "Someone must write about this." And here I am still unable to write about it. How do you write about it? How many words should you use?

"The longer the gunfire went on, the less likely it seemed that it would ever stop," the former prisoner said. Just beneath it you could still hear the sound of grown men begging for mercy. Then silence. A couple of days later the stink had become so un­bearable that no matter how empty your belly, you could not keep from retching.

The news of the massacre did not reach the outside world until 2001. Gradually, various accounts began to fill in the hideous puzzle. And so, corresponding with the end of any reported sightings of my father, we began to fear the worst. Then this ­tremendous news comes.

Too many facts. I am fed up of the facts. My father is not in the facts. Where is the man I liked to make laugh? Where is the man who would only respond to my letters when they were in Arabic? I would like to write a letter in Arabic. Where is the man who used to say the word "Patience" to me as if it were a vow? Where is the man to whom I had promised a granddaughter called Taswahin – which in Arabic means "a woman equal to any man" – the name he had always wanted for the daughter he never had. Where is the man who used to call me Sharh Elbal (literally "he who soothes the mind")? He liked to quote the repeated line in the Qur'an, from the chapter "Soothing": "With hardship comes ease. / With hardship comes ease."

Where is the man whose pipe stands in a cup with the five pencils I sharpen every morning? His coat hangs in my wardrobe. Maybe it still fits him.